Postgres hangs during VACUUM (autocommit = false)

I am having trouble with setting up a scheduled VACUUM. Since VACUUM needs
an exclusive lock, I can never get it to run. I am using persistant
connections from a web server and use a single module to make the
connection. I cannot autocommit because I need transactions.

So a ps gives several similar processes:

postgres 24298 0.6 1.1 6548 2964 ? S 14:00 0:15 postgres:
httpd epilogue [local] idle in transaction
postgres 24345 0.7 1.1 6496 2984 ? S 14:01 0:15 postgres:
httpd epilogue [local] idle in transaction
postgres 24391 0.9 1.1 6488 2900 ? S 14:02 0:19 postgres:
httpd epilogue [local] idle in transaction

I've tried doing a $dbh->commit() ; but that does no good. I read all the
posts I could find on this, but is there any way for me to schedule a VACUUM
that won't hang?

Autocommit is not an option.

Thanks!

Mark
epilogue.net